FragmentStatePagerAdapter.java revision 7dc96cc2410f551eefaa973ddc144146ad72d1ec
1/* 2 * Copyright (C) 2011 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17package android.support.v4.app; 18 19import java.util.ArrayList; 20 21import android.os.Bundle; 22import android.os.Parcelable; 23import android.support.v4.view.PagerAdapter; 24import android.util.Log; 25import android.view.View; 26import android.view.ViewGroup; 27 28/** 29 * Implementation of {@link android.support.v4.view.PagerAdapter} that 30 * uses a {@link Fragment} to manage each page. This class also handles 31 * saving and restoring of fragment's state. 32 * 33 * <p>This version of the pager is more useful when there are a large number 34 * of pages, working more like a list view. When pages are not visible to 35 * the user, their entire fragment may be destroyed, only keeping the saved 36 * state of that fragment. This allows the pager to hold on to much less 37 * memory associated with each visited page as compared to 38 * {@link FragmentPagerAdapter} at the cost of potentially more overhead when 39 * switching between pages. 40 * 41 * <p>When using FragmentPagerAdapter the host ViewPager must have a 42 * valid ID set.</p> 43 * 44 * <p>Subclasses only need to implement {@link #getItem(int)} 45 * and {@link #getCount()} to have a working adapter. 46 * 47 * <p>Here is an example implementation of a pager containing fragments of 48 * lists: 49 * 50 * {@sample development/samples/Support13Demos/src/com/example/android/supportv13/app/FragmentStatePagerSupport.java 51 * complete} 52 * 53 * <p>The <code>R.layout.fragment_pager</code> resource of the top-level fragment is: 54 * 55 * {@sample development/samples/Support13Demos/res/layout/fragment_pager.xml 56 * complete} 57 * 58 * <p>The <code>R.layout.fragment_pager_list</code> resource containing each 59 * individual fragment's layout is: 60 * 61 * {@sample development/samples/Support13Demos/res/layout/fragment_pager_list.xml 62 * complete} 63 */ 64public abstract class FragmentStatePagerAdapter extends PagerAdapter { 65 private static final String TAG = "FragmentStatePagerAdapter"; 66 private static final boolean DEBUG = false; 67 68 private final FragmentManager mFragmentManager; 69 private FragmentTransaction mCurTransaction = null; 70 71 private ArrayList<Fragment.SavedState> mSavedState = new ArrayList<Fragment.SavedState>(); 72 private ArrayList<Fragment> mFragments = new ArrayList<Fragment>(); 73 private Fragment mCurrentPrimaryItem = null; 74 75 public FragmentStatePagerAdapter(FragmentManager fm) { 76 mFragmentManager = fm; 77 } 78 79 /** 80 * Return the Fragment associated with a specified position. 81 */ 82 public abstract Fragment getItem(int position); 83 84 @Override 85 public void startUpdate(ViewGroup container) { 86 } 87 88 @Override 89 public Object instantiateItem(ViewGroup container, int position) { 90 // If we already have this item instantiated, there is nothing 91 // to do. This can happen when we are restoring the entire pager 92 // from its saved state, where the fragment manager has already 93 // taken care of restoring the fragments we previously had instantiated. 94 if (mFragments.size() > position) { 95 Fragment f = mFragments.get(position); 96 if (f != null) { 97 return f; 98 } 99 } 100 101 if (mCurTransaction == null) { 102 mCurTransaction = mFragmentManager.beginTransaction(); 103 } 104 105 Fragment fragment = getItem(position); 106 if (DEBUG) Log.v(TAG, "Adding item #" + position + ": f=" + fragment); 107 if (mSavedState.size() > position) { 108 Fragment.SavedState fss = mSavedState.get(position); 109 if (fss != null) { 110 fragment.setInitialSavedState(fss); 111 } 112 } 113 while (mFragments.size() <= position) { 114 mFragments.add(null); 115 } 116 fragment.setMenuVisibility(false); 117 mFragments.set(position, fragment); 118 mCurTransaction.add(container.getId(), fragment); 119 120 return fragment; 121 } 122 123 @Override 124 public void destroyItem(ViewGroup container, int position, Object object) { 125 Fragment fragment = (Fragment)object; 126 127 if (mCurTransaction == null) { 128 mCurTransaction = mFragmentManager.beginTransaction(); 129 } 130 if (DEBUG) Log.v(TAG, "Removing item #" + position + ": f=" + object 131 + " v=" + ((Fragment)object).getView()); 132 while (mSavedState.size() <= position) { 133 mSavedState.add(null); 134 } 135 mSavedState.set(position, mFragmentManager.saveFragmentInstanceState(fragment)); 136 mFragments.set(position, null); 137 138 mCurTransaction.remove(fragment); 139 } 140 141 @Override 142 public void setPrimaryItem(ViewGroup container, int position, Object object) { 143 Fragment fragment = (Fragment)object; 144 if (fragment != mCurrentPrimaryItem) { 145 if (mCurrentPrimaryItem != null) { 146 mCurrentPrimaryItem.setMenuVisibility(false); 147 } 148 if (fragment != null) { 149 fragment.setMenuVisibility(true); 150 } 151 mCurrentPrimaryItem = fragment; 152 } 153 } 154 155 @Override 156 public void finishUpdate(ViewGroup container) { 157 if (mCurTransaction != null) { 158 mCurTransaction.commitAllowingStateLoss(); 159 mCurTransaction = null; 160 mFragmentManager.executePendingTransactions(); 161 } 162 } 163 164 @Override 165 public boolean isViewFromObject(View view, Object object) { 166 return ((Fragment)object).getView() == view; 167 } 168 169 @Override 170 public Parcelable saveState() { 171 Bundle state = null; 172 if (mSavedState.size() > 0) { 173 state = new Bundle(); 174 Fragment.SavedState[] fss = new Fragment.SavedState[mSavedState.size()]; 175 mSavedState.toArray(fss); 176 state.putParcelableArray("states", fss); 177 } 178 for (int i=0; i<mFragments.size(); i++) { 179 Fragment f = mFragments.get(i); 180 if (f != null) { 181 if (state == null) { 182 state = new Bundle(); 183 } 184 String key = "f" + i; 185 mFragmentManager.putFragment(state, key, f); 186 } 187 } 188 return state; 189 } 190 191 @Override 192 public void restoreState(Parcelable state, ClassLoader loader) { 193 if (state != null) { 194 Bundle bundle = (Bundle)state; 195 bundle.setClassLoader(loader); 196 Parcelable[] fss = bundle.getParcelableArray("states"); 197 mSavedState.clear(); 198 mFragments.clear(); 199 if (fss != null) { 200 for (int i=0; i<fss.length; i++) { 201 mSavedState.add((Fragment.SavedState)fss[i]); 202 } 203 } 204 Iterable<String> keys = bundle.keySet(); 205 for (String key: keys) { 206 if (key.startsWith("f")) { 207 int index = Integer.parseInt(key.substring(1)); 208 Fragment f = mFragmentManager.getFragment(bundle, key); 209 if (f != null) { 210 while (mFragments.size() <= index) { 211 mFragments.add(null); 212 } 213 f.setMenuVisibility(false); 214 mFragments.set(index, f); 215 } else { 216 Log.w(TAG, "Bad fragment at key " + key); 217 } 218 } 219 } 220 } 221 } 222} 223